1. Field of the Invention
The present invention relates to a camera in which a detachable, interchangeable lens is attached to the camera body, and more particularly to a device for selecting an exposure mode for the camera.
2. Description of the Related Art
Conventionally, there are two kinds of interchangeable lenses, i.e., a first interchangeable lens and a second interchangeable lens. The first interchangeable lens has an aperture ring which can be set to an A-position, corresponding to an automatic setting mode in which an aperture value is automatically set from the camera body, and to M-positions, corresponding to a manual setting mode in which the aperture value is manually set. Namely, while the A-position is singular, there are a plurality of M-positions in which one of the numerals, which are formed on the aperture ring to indicate aperture values, is aligned with a mark formed on a surface of the lens barrel. The second interchangeable lens does not have such an aperture ring.
In a camera system in which the first interchangeable lens is used, in accordance with an operation of a control circuit provided in the camera body, a photographing operation can be carried out in a program mode or a shutter speed priority mode when the aperture ring is set to the A-position, and can be carried out in an aperture priority mode, a manual mode, or a bulb mode when the aperture ring is set to one of the M-positions. The camera system can be constructed to enable the aperture priority mode, the manual mode or the bulb mode to be selected, even when the aperture ring is set to the A-position. In this construction, however, because the aperture priority mode, the manual mode or the bulb mode can now be selected in both of the cases in which the aperture ring is set to the A-position or one of the M-positions, an operation of the mode selection becomes complicated. Therefore, usually, the camera is constructed so the selecting of the aperture priority mode, the manual mode and the bulb mode is prohibited when the aperture ring is set to the A-position.
Conversely, in a camera system in which the second interchangeable lens is used, in accordance with an operation of a control circuit provided in the camera body, a photographing operation can be carried out in the program mode, the shutter speed priority mode, the aperture priority mode, the manual mode, or the bulb mode. In this camera system, a setting device, by which these modes are set, is not provided in the interchangeable lens, but both of the setting operations, in which one of the modes is selected, and the aperture value are set by a setting device provided in the camera body.
If the second interchangeable lens is attached to a camera body of a camera system, which was originally designed for using the first interchangeable lens, the control circuit provided in the camera body automatically assumes that the aperture ring is set to the A-position. Accordingly, in this camera system, there is a problem in which the aperture priority mode, the manual mode and the bulb mode are not available for selection. Conversely, if the first interchangeable lens is attached to a camera body of a camera system, which was originally designed for using the second interchangeable lens, then the aperture priority mode, the manual mode and the bulb mode can be selected when either the aperture ring is set to the A-position or one of the M-positions, which has a different aperture value setting operation than the A-position; thus both aperture value setting operations are complicated.